1. Field of the Invention
This invention relates to an information storage medium apparatus, and more particularly to an information storage medium apparatus that can be applied to information processing apparatus other than a specified reproduction-only apparatus.
2. Description of the Prior Art
In recent years, optical discs have been widely used as information storage media that reproduce image information or acoustic information. The recording or reproduction of such information is performed by applying laser beams to a rotating optical disc. In comparison with magnetic information storage media, the optical discs have larger storage capacities per unit area, and stable low-noise reproduction characteristics. The optical disc can record or reproduce information with a non-contact operation, resulting in the following advantages. Specifically, no wear can occur in the storage medium surface and the laser-beam applying head. Further, optical recording or reproduction is substantially independent of surrounding disturbances as compared to magnetic processing.
In general, optical discs may be classified into the following three types in terms of their applications and structures. The first type thereof is a reproduction-only optical disc which can only reproduce the previously recorded information. The first-type optical disc includes three different discs, such as a VD (video disc), a CD (compact disc) and a CD-ROM (CD read-only memory). The VD has image information recorded thereon in analog signals, and the CD has acoustic information recorded thereon in digital signals. The CD-ROM has the coded information of a computer or the contents of a dictionary recorded thereon in digital signals. The copies of these discs can be easily formed by molding with a stamper. Thus, such discs can be mass-produced and provided at lower prices. As a result, these discs have been widely used in various applications. The first-type optical disc is usually incorporated in a protective container such as a plastic case. When in use, the optical disc per se is taken out of the container, and is placed in an reproduction-only apparatus.
Further, the first-type optical disc consists of the following three layers. Specifically, a transparent polycarbonate disc of about 1.2 mm thick is prepared to form a large number of pits corresponding to signals on the surface of the disc. An aluminum thin film, which serves as a reflector layer, is sputtered on the surface of the polycarbonate disc. A protective layer of hard resin is then formed on the reflector layer. A second-type optical disc is an additional writing-type optical disc on which information can be additionally written. However, additional writing can be made only once in the same area because written information cannot be erased. Thus, the second-type optical disc has been adapted to applications in which the operator must additionally write information in a blank area as required. The added information can be stored over long period. A third-type optical disc is a rewritable-type optical disc on which information can be recorded and erased repeatedly. The third-type optical disc can record information of very high density. Thus, the discs of this type have been used as large-capacity storage media in information processing systems.
The additional writing-type optical disc and the rewritable-type optical disc are usually incorporated in a cartridge 21, as shown in FIG. 6. This is because the surface of the optical disc must be protected from dust and external forces. When in use, the cartridge 21 is inserted in an information recording and reproducing apparatus in the direction of arrow A. In this case, the optical disc remains in the cartridge 21 without being taken out of it. When the cartridge 21 is set on a prescribed position in the apparatus, a shutter 22 is automatically opened in the direction of arrow B. As a result, a part of the optical disc is exposed through a window 23. Namely, the optical disc is protected from unnecessary exposure.
In the case of the reproduction-only optical disc, the optical disc is taken out of its container, and placed on a reproduction-only apparatus. Specifically, in the reproduction-only apparatus, an optical disc 24 is set on a turntable 25 and secured by a depressing member 26, and then rotated by an electric motor 27, as shown in FIG. 7. Therefore, the reproduction-only optical disc cannot be applied to an information recording and reproducing apparatus. This causes many disadvantages when the optical discs of various types must be handled.